In a Winchester type disk drive, a positioner carries a read/write head above the magnetic material coated surface of a disk. The positioner is rotated by an actuator mounted to the chassis of the disk drive. The actuator locates the positioner in response to an address signal so that the heads become properly located along an addressed track within the data zone of the disk.
When the disk drive is shut down, it is desirable to move the positioner to a position which causes the heads to be removed from the data zone to a landing zone. This removal of the heads to the landing zone is widely known in the art as "parking" the heads. Once the heads are parked, it is desirable to latch the positioner in its parked position. With the positioner latched in the parked position, the positioner is unable to stray back into the data zone in the event of unintentional shock and vibration acting upon the disk drive. Such unintentional shock and vibration may come from the casual moving of the disk drive or equipment containing the disk drive.
To latch the positioner in the parked position, a solenoid activated lock may be provided for engaging either of the positioner or actuator. For example, in U.S. Pat. No. 4,807,072 (hereinafter "the '072 patent"), a head positioner control mechanism with head locking for a magnetic disk drive is disclosed. The transducer head is locked by a locking lever which pivots in a plane parallel to the disk plane for movement in and out of locking engagement with a latching member jointly rotatable with the head arm positioner. A solenoid holds the locking lever out of engagement with the latching member during data transfer between the disk and head. Upon completion of data transfer or when power is removed from the disk drive, the solenoid becomes de-energized thereby permitting the locking lever to be sprung into locking engagement with the latching member. Since the latching member is jointly rotatable with the head positioner, the positioner is locked in place.
A disadvantage and limitation of the device disclosed in the '072 patent is that during operation of the disk drive, an electrical current needs to be continuously applied to the locking solenoid to keep the locking lever retracted. A loss of this current during normal disk drive operation can cause unwanted interaction of the locking lever with the latch arm which may result in catastrophic failure of the disk drive. This current also generates heat in the solenoid windings which may, over a period of time, cause failure of the solenoid. Furthermore, the holding current during operation of the solenoid increases power usage of the disk drive.
The disadvantages and limitations of the device described in the '072 patent are specifically addressed by the electromechanical latch described in U.S. Pat. No. 4,989,108 (hereinafter "the '108 patent"). The latch described in the '108 patent is of the type where the latching member is removed from its latching position upon a current being applied to the electromechanical latch and wherein the latch remains removed from the latching position when the current is removed.
More particularly, the electromechanical latch described in the '108 patent includes a solenoid having an armature moveable from a normally biased first position to a second position in response to an electrical current being applied to the solenoid, and means for holding the armature in the second position to allow subsequent removal of the current from the solenoid. When the armature is in its first position, it is adapted for latching a positioner in a parked position. The armature is not interactive with the positioner when its in its second position. The electromechanical latch further includes means for releasing the holding of the armature in response to the positioner returning to its parked position, whereby the armature returns to its normally biased first position to latch the positioner.
Thus, the device of the '108 patent advanced the state of the art from that disclosed on the '072 patent in that the current need be applied to the solenoid only for moving the armature to its second position to release the positioner. Once in the second position, the armature is held mechanically. This advance in the state of the art then allowed the current to be removed from the solenoid with the holding means holding the armature in a position which is non-interactive with the positioner during normal operation of the disk drive.
In some prior art devices in which a current releases the lock and a mechanical hold feature allows removal of the current, the positioner may need to have slight over travel to trigger a hook mechanism which captures the positioner in its parked position. This over travel may cause some of the data zone to be wasted for use in conjunction with the over travel. Should the positioner fail to over travel, the hook mechanism will not engage the latch arm and the positioner will not be locked. Furthermore, to disengage the positioner, a disengage current sufficient to overcome the magnetic attraction between the core and the armature at a specified range of voltages would be required. It is possible that a latch may be "sticky" and not respond to the disengage current.